The disclosure relates to a hydrostatic drive, in particular a hydrostatic fan drive.
In the case of hydrostatic drives, it is known for a variable-displacement pump and a motor to be connected in a closed circuit via two working lines. Here, a hydraulic adjustment device is provided for adjusting the swept volume of the variable-displacement pump. Here, “swept volume” is to be understood to mean the quantity delivered by the variable-displacement pump per revolution. Adjustment pressure medium is supplied to the adjustment device by means of a feed pump which is driven together with the variable-displacement pump for example by an internal combustion engine. The adjustment pressure medium is supplied to or discharged from the adjustment device as required by means of a directional valve. For example, the pivot angle of the variable-displacement pump, which is in the form of a swashplate-type axial piston pump, is set in this way.
In order that a certain maximum pressure value is not exceeded in that working line of the hydrostatic drive which is conducting the high pressure, pressure cut-off valves are known which limit the maximum adjustment pressure when the high pressure reaches the maximum pressure value. In this way, the adjustment device of the pump is relieved of pressure, such that the latter reduces its swept volume, whereby a limit value for the high pressure in the working line is not exceeded.
Document DE 10 2004 061 861 B4 discloses a hydrostatic drive of said type with a pressure cut-off valve. Since the variable-displacement pump or the adjustment device thereof can be pivoted about, the direction of rotation of the motor can be changed, which results in a switchover of the working line that conducts high pressure. In order that the pressure cut-off valve nevertheless always reduces the adjustment pressure as a function of the high pressure, a shuttle valve is positioned upstream of the control side of the pressure cut-off valve.
Document DE 10 2010 020 528 A1 presents a reversible hydrostatic drive. In said document, the hydrostatic drive is used for driving a fan impeller. Furthermore, the presented fan drive has a pressure regulating valve which can be adjusted by means of a proportional magnet and which serves for regulating the adjustment pressure in each case one of two adjustment chambers that are separated from one another by an adjustment piston, whereas the respective other adjustment chamber is charged with feed pressure. Thus, the pivot angle of the variable-displacement pump is influenced through adjustment of the pressure regulating valve.
A disadvantage of such hydrostatic drives is that, in the case thereof, simple regulation of the high pressure is not possible.
By contrast, it is the object of the disclosure to provide a hydrostatic drive, in particular a hydrostatic fan drive, with which it is possible, with little outlay in terms of apparatus, for the maximum high pressure to be varied in a simple manner during operation.